1. Technical Field
The present disclosure relates to a vehicle technology field, more particularly to a drive system of an electric vehicle.
2. Description of the Related Art
With increasing of fuel price and environmental pollution caused by traditional vehicles, electric vehicle has attracted most attention. An electric vehicle has a power source from a power battery, driven by an electric motor, thus breaking away from limitation of an engine and reducing the environmental pollution.
Traditionally, an electric vehicle may be driven by a drive motor and a reducer with a constant ratio. As widely known, the drive motor has a large output torsion and low efficiency at a low rotational speed. With the increasing of rotational speed of the drive motor, the efficiency is increasing as well, but an output torsion is much lower. With reference to the electric vehicle including a reducer with a constant ratio, for the reducer with a great torsion, the efficiency is increasing slowly with the increasing of the rotational speed of the drive motor, as a result power consumption of the vehicle is quite big at a high ground speed; for the reducer with a high rotational speed, the efficiency is increasing fast with the increasing of the rotational speed of the drive motor, however, due to the low transmission ratio of the reducer, the torsion transmitted to the vehicle wheels is too low to satisfy starting and climbing of the vehicle. As a result, the power consumption of the vehicle is quite big at a low ground speed. For example, an electric bus has a very frequent acceleration in parking and starting which may cause low efficiency of the drive motor. Therefore, the drive system of a traditional electric vehicle has difficulties to simultaneously meet the work conditions of a low ground speed and a high ground speed, and has a drive motor with a low efficiency, which may shorten the endurance mileage of an electric vehicle if power storage of a battery is not changed. As a result, the traditional electric vehicle is not able to meet complicated driving conditions.